Unit 3 AOS 1 - Nucleic acids and Proteins Flashcards
The proteome
The complete set of proteins expressed by the genome at a particular time.
How do cells create proteins?
Proteins are made of amino acids linked by peptide bonds to form a polypeptide chain, which folds into a specific shape for the protein to become functional.
R group
Determines the chemical properties of the amino acid and the folding of the final protein.
Primary structure
A sequence of a chain of amino acids that make up a polypeptide chain
Secondary structure
Folding and coiling of the polypeptide chain due to hydrogen bonds. Structures can be an alpha helix, beta sheet or a random coil.
Tertiary structure
The 3D shape of a functional protein from the folding of the polypeptide chain, determined by the “R” group.
Quaternary structure
Consists of 2 or more polypeptide chains, held together by covalent bonds.
Conjugated proteins
Protein joined in an interaction with other (non-polypeptide) chemical groups.
How does DNA code for a protein?
- In the nucleus, DNA for a gene is copied through transcription, the gene copy is pre-mRNA.
- Pre-mRNA then undergoes RNA processing to become mRNA.
- mRNA leaves the nucleus and is translated into protein at the ribosomes.
What are the coding regions for eukaryotes?
Introns (non-coding section) and Extrons (coding sections)
Promoter (TATA box) function?
Upstream of the coding region and contains a DNA sequence that RNA polymerase binds to start transcription.
Process of Transcription
Operator (prokaryotes)
Site where repressor proteins can bind to inhibit gene transcription.
Terminator
DNA sequence that signals for the end of transcription.
RNA and DNA order of reading?
RNA: 3’ to 5’ end
DNA: 5’ to 3’ end
DNA’s two antiparallel strands
1) coding strand (5’ to 3’) and determines correct nucleotide sequence for mRNA.
2) template strand (3’ to 5’) which is transcribed into mRNA.
Process of Transcription
1) RNA polymerase binds to the promoter region and the DNA unwinds and strands seperate.
2) RNA polymerase moves along the template strand (3’ to 5’). Free-floating RNA nucleotides bind to complementary bases on the DNA strand, generating pre-mRNA that runs in a 5’ to 3’ direction.
3) At the terminator region, RNA polymerase and pre-mRNA strand detach from the DNA, and the DNA unwinds.
4) In eukaryotes, the pre-mRNA then undergoes RNA processing to make mRNA which can then leave the nucleus.
Where in the cell does Transcription occur?
In the nucleus of the cell.
RNA processing
- A methyl cap is added to the 5’ end which protects mRNA from degradation and helps attach mRNA to ribosomes during translation.
- A poly (A) tail is added to the 3’ end which protects mRNA from degradation and facilitates the export of mRNA from the nucleus.
Splicing
- Introns are removed ( as they are non-coding sections ) and the exons are spliced together ( they are coding sections ). This process is aided by spliceosomes.
- As the exons are spliced together, this provides the code for protein synthesis.
Alternative splicing
To make multiple different proteins from the same gene, it’s possible to change which exons are spliced into the processed mRNA. This changes the order of the exons in the final mRNA.
mRNA
-After RNA processing or post transcriptional modifications, the pre-mRNA is now mRNA.
-This mRNA can now be transported out of the nucleus to the ribosome to be translated into a polypeptide.
Process of Translation
- mRNA strand enters the ribosome.
- Ribosome reads codon in 5’ - 3’ direction.
- tRNA delivers amino acids by matching complementary anticodons with mRNA codons.
- Peptide bonds form between amino acids.
- Stops at stop codon, releasing polypeptide.
Translation occurs at the ribosome
- Ribosomes are tightly folded rRNA that can be found free-floating in the cytosol or attached to the rough endoplasmic reticulum.
- Amino acids are joined together by the ribosome which is reading the instructions for the mRNA.
Where in the cell does translation occur?
cytosol
What is gene regulation?
The process by which cells control the expression of genes, turning them on or off as needed.
What is a structural gene?
A gene that codes for a protein product required for the functioning of the cell.
What is the role of regulatory genes?
Regulatory genes code for proteins that promote or inhibit the expression of structural genes.
What is the trp operon?
A group of genes that code for enzyme proteins required to synthesize the amino acid, tryptophan.
List the five structural genes in the trp operon.
- trpE
- trpD
- trpC
- trpB
- trpA
What is the function of the leader region in the trp operon?
It sits between the operator region and the structural genes and is involved in regulating transcription.
Where is the regulatory gene trpR located?
Upstream of the structural genes in the trp operon.
What does the trpR gene encode?
A repressor protein.
How does repression occur in the trp operon?
High levels of tryptophan cause the repressor protein to bind to the operator, blocking transcription.
What happens when tryptophan levels are low?
The inactive repressor cannot bind to the operator, allowing RNA polymerase to transcribe the structural genes.
What is attenuation in the context of the trp operon?
A regulatory mechanism that stops transcription early in response to high levels of tRNA-bound tryptophan.
True or False: Attenuation occurs because transcription and translation are separated by a nuclear membrane in prokaryotes.
False
What happens when the ribosome reaches the leader region during attenuation?
If tRNA-bound tryptophan is high, the ribosome translates the two trp codons quickly, forming a terminator loop.
What is the outcome of the terminator loop formed during attenuation?
It causes the mRNA to detach from the DNA and results in a short (attenuated) mRNA sequence.
What are the two main mechanisms by which high levels of tryptophan regulate the trp operon?
- Repression
- Attenuation
Fill in the blank: The _______ protein blocks RNA polymerase from transcribing the structural genes when tryptophan levels are high.
[repressor]
What is the significance of cells regulating protein expression?
It allows for cell specialization and energy conservation.
What is the function of the rough endoplasmic reticulum?
Folds proteins synthesised from the attached ribosomes and transports them to the Golgi apparatus.
What does the Golgi apparatus do?
Modifies and packages proteins for export from the cell.
What are secretory vesicles?
Fuse to the plasma membrane to export substances via exocytosis.
What is the role of ribosomes?
Synthesise protein polypeptides from amino acids.
What is exocytosis?
The bulk movement of substances out of the cell via vesicles.
